Amazing Arachnids: The Lace-Weaver Spiders

Amazing Arachnidsis a new, month-long series from Princeton Nature. Each week, we’ll highlight one of the unique arachnids found in Jillian Cowles’ richly illustrated and up-close look at the secret lives of spiders.

Adapted from page 229 of the text:

Broad, black chelicerae and a stocky build give members of the family Amaurobiidae a powerful appearance suggestive of bulldogs. The imposing physique of these spiders contrasts with the delicate beauty of their webs, built of woolly cribellate silk. These characteristic webs give this family its name “lace-weaver spiders” or “hacklemesh weavers.” The cribellate silk of the web radiates out from a tunnel retreat, where the spider lies in wait. Insects become tangled in these hackled threads, giving time for the spider to rush out from its hiding place and catch the prey.

Amaurobius has a truly remarkable natural history in regard to its reproduction. In the case of Amaurobius ferox (an introduced species from Europe reportedly found in southern California), the mother spider lays her first clutch of eggs and stays nearby to guard them until the babies hatch. This maternal behavior is consistent with many other species of arachnids and is therefore hardly noteworthy. But then it gets interesting. After the spiderlings emerge from the egg sac, they interact with their mother, and she is induced by this interaction to lay a second clutch of eggs. This time, the eggs are laid before they are mature, and consequently this clutch of eggs serves as food for the spiderlings that hatched from the first clutch. This is referred to as trophic egg laying and is a strategy employed by several other species of animals, including some species of poison dart frogs. The spiderlings that receive this food are heavier and have a higher survival rate than spiderlings deprived of the trophic egg meal.

Callobius arizonicus. Callobius are found in cool areas, such as the mountains of Arizona and the forests of California.

But the mother spider’s sacrifice does not end there. The mother and her offspring interact further, and this time she actually appears to solicit her babies to feed on her. This the babies do, collectively killing and feeding on their mother. This matriphagy appears to be regulated by the life stage of the spiderlings, the reproductive state of the mother, and the behavioral interactions of the mother and her young. The spiderlings derive considerable benefit from this behavior. They are heavier and larger at the time they disperse compared with spiderlings deprived of their mother as food, including groups of spiderlings given an abundance of other prey to eat.

Finally, the matriphagous spiderlings have a longer period of social behavior, compared with the nonmatriphagous spiderlings. The subsocial spiderlings live together through several instar stages on the web of their mother, cooperatively killing prey and sharing it. The maternal web appears to provide a superior platform for the offspring to detect and cooperatively kill prey, as compared with webs that the spiderlings construct themselves. Prey that would be too large for one or two spiderlings to overcome is killed by groups of spiderlings, and that prey is shared even with those that did not take part in that particular kill. The spiderlings appear to use coordinated teamwork to subdue prey that is up to 10 times the size of any individual spiderling. Cooperative prey capture increases predation efficiency and survival of all the spiderlings.

Most of the members of the family Amaurobiidae live in cool, moist habitats, making their webs under debris, in caves, or in the nooks and crannies of trees. California boasts the greatest diversity of these spiders in the United States. In the arid southwestern states, Callobius arizonicus lives principally at higher elevations where it is cooler and moister. Found under rocks and dead wood, several individual Callobius spiders may share a single shelter. Only centimeters may separate their webs, indicating some degree of tolerance between individuals of the same species. Also like Amaurobius, Callobius guards her egg sac, which is produced in the shelter of her refuge. But in the case of Callobius, it is unknown whether the mother spider feeds her young.

The American Southwest is home to an extraordinary diversity of arachnids, from spitting spiders that squirt silk over their prey to scorpions that court one another with kissing and dancing. Amazing Arachnids presents these enigmatic creatures as you have never seen them before. Featuring a wealth of color photos of more than 300 different kinds of arachnids from eleven taxonomic orders–both rare and common species—this stunningly illustrated book reveals the secret lives of arachnids in breathtaking detail, including never-before-seen images of their underground behavior.

Amazing Arachnids covers all aspects of arachnid biology, such as anatomy, sociality, mimicry, camouflage, and venoms. You will meet bolas spiders that lure their victims with fake moth pheromones, fishing spiders that woo their mates with silk-wrapped gifts, chivalrous cellar spiders, tiny mites, and massive tarantulas, as well as many others. Along the way, you will learn why arachnids are living fossils in some respects and nimble opportunists in others, and how natural selection has perfected their sensory structures, defense mechanisms, reproductive strategies, and hunting methods.

Covers more than 300 different kinds of arachnids, including ones new to science

Features more than 750 stunning color photos

Describes every aspect of arachnid biology, from physiology to biogeography

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